The invention relates to testing components in digital imaging devices.
Digital image processing involves capturing, manipulating and analyzing digital information. A digital imaging device, such as a digital camera, can capture optical images and convert them to digital format. In a typical digital camera, optics are used to focus an optical image onto an array of pixel sensors (arranged in rows and columns) that electrically capture the image. The sensors are electrically coupled to one or more analog-to-digital (A/D) converters that convert the analog sensor signals to digital signals that are supplied to other components for further processing, including transmission to a computer. Referring to FIG. 1, for example, in an imaging system 10, a digital camera 12 can capture an optical image 11 and transmit a stream of data representing the image 11 to a computer 14, where the image data can be further processed.
After manufacture of a digital imaging device, components (including analog components such as the pixel sensors, associated circuitry, amplifiers, and A/D converters) in the device are tested to ensure functionality. Faults that can occur in the pixel sensor array and associated circuitry include stuck-at faults (such as a sensor bit or a wire being stuck at a fixed voltage) and shorts (such as two columns of sensors being shorted). Other components that can be tested include amplifiers (which are set to have predetermined gain values) and A/D converters (which for optimal performance must have a predetermined linearity across a range of input and output signal values).
One system for performing tests includes using high precision voltage supplies in the tester system to apply predetermined voltages to the sensor array of a digital imaging system and checking the output values from the A/D converters. Given an applied input voltage, a predetermined output voltage is expected from the A/D converter. A test system capable of generating high precision voltage values (e.g., voltages precise to the millivolt range) is typically needed to perform accurate testing of the analog components of the digital imaging system.
To check if the A/D converters in the device have the desired linearity, a range of input voltages can be applied to the sensor array, with the output voltages from the A/D converters checked. Again, to ensure accurate testing, the applied voltages typically are based off high precision supply voltages generated in the tester system.
By using high precision supply voltages in tester systems, test cost and time are increased. Testers with high precision voltage supplies are typically costly. Further, during the testing sequence, a waiting period is required after a change in the applied voltage to allow the signal time to settle. With the relatively large number of test cycles involved in testing a sensor array in a digital imaging device, the test time can be dramatically increased which raises testing cost.
The invention generally relates to testing components in a digital imaging system using test circuitry having a reference voltage generator.
In general, in one aspect, the invention features a digital imaging device including an array of sensors having data lines coupled to the sensors. Receiving logic is coupled to sense voltages on the data lines. A test circuit includes a reference voltage generator that generates a plurality of reference voltages in response to an applied differential voltage. A plurality of test sensors are electrically coupled to corresponding reference voltages, each test sensor electrically coupled to a data line and receiving a voltage based on its coupled reference voltage.
Other features will become apparent from the following description and from the claims.